Multistable mechanical metamaterials can store information in their configuration — which of several stable states each unit cell occupies. Switching between states propagates as a kink: a transition wave that converts cells from one state to another as it passes through the structure. The kink is the write operation. Where it stops is the stored bit.
Controlling where kinks stop — and making them start again — has required either direct mechanical actuation at each cell or brute-force deformation of the entire structure. Neither scales.
Ferracin, Jin, Tournat, and Raney (arXiv:2603.02433, March 2026) solved this with phonons. They pinned kinks at intentional defects in the metamaterial — local variations in stiffness or geometry that create energy barriers the kink cannot cross passively. The kink arrives at the defect and stops. Information is stored.
To release the kink, they send phonon pairs from the boundary. The two phonons have slightly different frequencies, creating a beating envelope whose frequency matches the pinned kink's translational mode — the vibrational mode that corresponds to the kink moving forward. This mode sits inside a phononic band gap, meaning it can't be excited by a single phonon at that frequency (band gap phonons don't propagate). But the beating envelope of two band-edge phonons reconstructs the forbidden frequency through interference. The resonant coupling transfers energy specifically to the kink's translational degree of freedom, pushing it over the defect barrier. The kink resumes propagation.
The inspiration is explicit: phonon-dislocation interactions in crystalline solids, where lattice vibrations can help dislocations overcome Peierls barriers. The metamaterial scales this interaction up to centimeter-scale structures where it can be engineered and controlled.
The result is a mechanical memory that reads and writes with sound. Kinks store bits. Defects are addresses. Phonon pairs are the access signal. The entire operation is mechanical — no electronics, no external actuation, just structured vibration interacting with structured instability.
Ferracin, Jin, Tournat, and Raney, "Phonon controlled mechanical memory via pinning and depinning of transition waves," arXiv:2603.02433 (March 2026).